The present invention relates to an automatic film winding system for cameras.
Various types of automatic film winding systems or devices have been devised and demonstrated. In general, they comprise a film transport or winding system and a perforation sensing system. The film transport or winding system includes an electric motor drivingly coupled through a reduction gear means to a film winding means. The perforation sensing system detects the length of the film advanced by the film transport system.
A typical prior art automatic film winding system will be described below in conjunction with a 110-size film. The film is loaded in the camera body. When a shutter button is depressed, a shutter mechanism accomplishes one exposure operation. Then, an electric switch coupled to the shutter mechanism is turned on so that a power supply is automatically connected to the motor and subsequently the film is advanced from the pay-off chamber to the take-up chamber of a film cartridge. When the perforation sensing system has detected a predetermined number of perforations of the film which corresponds to the width or height of a frame, the displacement of a mechanical sensing element is transmitted through a linkage comprising a few components to the reduction gear means, causing it to be disconnected from the electric motor. Thus the film transport is interrupted; that is, the film has been advanced by one frame. The same steps are repeated every time when one exposure is made.
In a system disclosed in U.S. Pat. No. 4,084,169, after the perforation sensing system of the type described above has detected a predetermined number of perforations, an electric switch is operated through a linkage so that the electric motor can be stopped electrically.
In the prior art perforation sensing systems, a perforation sensing element is normally brought into contact with the surface of a film and engages with perforations as the film is advanced. As a result, the sensing element very frequently causes damage to the film surface and the perforations. Furthermore, particles scratched off from the film surface by the sensing element tend to cause serious damage to the emulsion on the film. In addition, every time when the film is advanced, it has different inertia. As a result, an over-advancement that is, the phenomenon that the film is still advanced even after the perforation sensing system has counted or detected a predetermined number of perforations, results. Alternatively, an under-advancement that is, the phenomenon that the film is not advanced by a predetermined length, results because the electric motor stops in response to the output from the perforation sensing system generated erratically before the system detects a predetermined number of perforations. The prior art perforation sensing systems have a further drawback in that the wear of their mechanical parts is unavoidable and subsequently erratic detections result, causing over- or under-advancements.